This invention relates to improved vibration dampers for use with oscillating bodies and particularly to torsional vibration dampers of the type to be mounted on the end of a crankshaft of an internal combustion engine. This invention also relates to the method of making such vibration dampers.
In the prior art, various type vibration dampers have been used to damp or attenuate torsional vibrations generated during the operation of various internal combustion engines. These dampers include a central metallic core or hub which is mounted to the crankshaft of the engine by means of bolts or the like and an outer inertia mass in the form of a relatively thick metal ring for the purpose of counteracting or counterbalancing the forces existing due to the rotation of the shaft. One well known type of damper used for many years is the viscous damper which employes a damping fluid such as silicone oil in a completely sealed unit with the torsional vibrations of the crankshaft being absorbed by the shear resistance of the viscous fluid.
More recently another type damper known as a viscous rubber damper has been developed in which the inner hub and the outer inertia ring are separated by an elastic damping member or spacer comprising a layer of flexible resilient elastomeric material such as rubber. In this type damper the torsional vibrations are absorbed not only by the shear resistance of the viscous fluid but also by the hysteresis of the rubber. Exemplary of the viscous rubber type torsional vibration dampers are those disclosed in U.S. Pat. No. 3,603,172 and 3,707,031 to Hall and U.S. Pat. No. 3,678,782 to Hidemasa.
In another type damper not employing a viscous liquid, the elastic damper member is retained between the inner hub and the outer inertia ring under a high degree of compression usually from about 25 to about 50 percent of the original thickness of the elastic member.
Each of the beforenamed type dampers have disadvantages which adversely affect their operation. For example, the sealed viscous vibration dampers are costly to manufacture and since the unit is sealed, it is difficult to determine when there is a malfunction. The nonviscous type dampers have also not been completely satisfactory in many instances. Since the elastic damper member is held in position between the inner hub and the outer inertia ring solely because of the high degree of compression, the rubber may tend to roll out from between the inter faces with the metal elements. This is due primarily to the torque impulses created during the operation of the engine which may cause the rubber to flex as much as 200 times per second. This loss in rubber results in a rather drastic change in dynamic characteristics of the damper. Furthermore, in previous vibration dampers it has been common to use rubbery polymeric material such as natural rubber or synthetic rubber which do not maintain the desirable characteristics of dynamic stiffness or modulus and damping over a wide temperature range. This has been particularly true of dampers used on turbo-charged engines.
The above-mentioned difficulties of the prior art have been overcome by the present invention by use of an improved vibration damper and method of making same as will be hereinafter described.